Field of the Invention
The present invention relates to a plugged honeycomb structure and a plugged honeycomb segment. More particularly the present invention relates to a plugged honeycomb structure and a plugged honeycomb segment improved in a PM accumulation limit.
Description of the Related Art
In recent years, there has been a demand for the reduction in a fuel consumption of an automobile from the viewpoints of influences on the global environment and resource saving. This leads to a tendency of using internal combustion engines with a good thermal efficiency, such as a direct injection type gasoline engine and a diesel engine, as a power source for an automobile.
Meanwhile, these internal combustion engines have a problem that a soot is generated during a combustion of the fuel. A countermeasure has been then required from the viewpoint of an air environment to remove toxic components included in an exhaust gas and to avoid the emission of a particulate matter (hereinafter this may be called “a PM”), such as a soot or an ash, to the air.
Especially there is a global tendency of tightening the regulations on a removal of the PM emitted from a diesel engine. Then a honeycomb-structured wall flow type exhaust gas purification filter has attracted the attention as a trapping filter (this may be called a “DPF”) to remove the PM, and various systems for the filter have been proposed. Such a DPF is typically configured so that a plurality of cells serving as a through channel of a fluid is defined by a porous partition wall, and by plugging the cells alternately, the porous partition wall making up the cells functions as a filter. A pillar-shaped structure including a plurality of cells defined by a porous partition wall may be called a “honeycomb structure”. Then a honeycomb structure including cells whose open ends are plugged with plugging portions may be called a “plugged honeycomb structure”. A plugged honeycomb structure is widely used as a trapping filter, such as a DPF. As an exhaust gas containing a particulate matter flows into the plugged honeycomb structure from the inflow end face (first end face) of the plugged honeycomb structure, the particulate matter in the exhaust gas is filtered when the exhaust gas passes through the partition wall, and the purified gas is emitted from the outflow end face (second end face) of the plugged honeycomb structure.
Conventionally a plugged honeycomb structure includes the cells, such as quadrangular cells, hexagonal cells, and HAC cells (cells having the geometry that is the combination of octagons and quadrangles). Recently new plugged honeycomb structures which include the combination of cells of different shapes or devise the position of plugging have been developed (see Patent Documents 1 and 2). Such plugged honeycomb structures allow a pressure loss at the initial stage of use to be reduced, and allow a pressure loss when a PM is accumulated to be reduced, and then allow cracks during burning of the PM to be suppressed and a lot of ash at the partition wall to be accumulated.
[Patent Document 1] JP-A-2014-200741
[Patent Document 2] JP-A-2015-029939